There have been many attempts in the past to improve the safety accorded to occupants of automobiles when involved in an accident. A portion of these attempts have dealt with the provision of various safety devices in the passenger compartment, most commonly by implementing passenger restraint systems such as safety belts and/or harnesses. However, during the 1970s some automobile manufacturers began supplementing these typical passenger restraining systems with air bags located throughout the passenger compartment to enhance the safety features of the automobile.
Many developments were made regarding the use of air bags during the 1970s, partially as a result of an increased awareness of the need for increased passenger safety as well as in anticipation of possible government regulations requiring that air bags be employed in all automobiles. Although a large amount of development was directed towards automobile air bags during this time period, due to various factors, these activities subsided and have only again begun to increase.
The general concept of an automobile air bag is to provide an inflatable structure that is responsive to an impact which will inhibit the forward motion of a passenger to reduce the likelihood of suffering severe injury when involved in an accident. Although the air bag is quite simple in concept, there have been numerous developments regarding the manner in which the air bag is inflated, including regulation of the flow rate of the materials injected therein.
In U.S. Pat. No. 4,018,457 to Marlow, issued Apr. 19, 1977, an air bag safety apparatus is disclosed in which there are basically two flow rates for the material being injected into the air bag--one for low impact collisions and another for high impact collisions. The Marlow apparatus includes an outer containment which stores a gas under pressure for inflating an air bag. Enclosed within this outer containment is a propellant containment which stores a propellant charge. In a low impact collision, one ignitor activates the propellant charge, causing an increase in pressure within the propellant containment. This increase in pressure eventually ruptures a disk which isolates the propellant containment from both the outer containment and a ramming member. Upon rupture of this disk, exhaust gases from combustion of the propellant charge mix with the gas stored in the outer containment. In addition, the rupture also directs a ramming member towards a disk which ultimately isolates the outer containment from the air bag. The ramming rod breaks this disk and allows the mixed gasses to flow into the air bag. The operation of the apparatus for a high impact collision merely adds the additional step of firing a second ignitor which, summarily, causes the propellant charge to burn at a faster rate, thereby increasing the flow rate into the air bag. Regardless of whether one or two ignitors are activated in the Marlow apparatus to ignite the propellant, the activation is ultimately produced by an electrical signal. Furthermore, even though the Marlow patent discloses two flow rates into an air bag for low and high impact collisions, there is no disclosed means of increasing the flow rate into an air bag after an initial volume of material has been injected therein.
U.S. Pat. No. 4,050,483 to Bishop, issued Sept, 27, 1977, discloses an inflation apparatus which incorporates a surge delay. In this apparatus, there is a cylinder containing a volume of gas under pressure. At the discharge end of this cylinder, a rupture disk separates the cylinder from the manifold connecting the cylinder to the air bag. The rupture disk is coupled with a device capable of generating a force sufficient to break the rupture disk. When a collision is sensed, a signal is sent to the device to rupture the disk and thereby allow gas to begin to flow from the cylinder, through a discharge manifold, and into the air bag. The rate of deployment of the air bag at this juncture is reduced since the flow of gasses prior to the ignition of the propellant charge does not generate sufficient pressure to rupture a disk located in the manifold's main flow channel. Consequently, the initial flow of gasses is through secondary flow channels in the manifold. Upon breakage of the rupture disk allowing the initial flow of gas into the air bag, there is a predetermined time delay after which a second signal is sent to the end of the cylinder opposite the discharge manifold to activate a propellant charge contained in an isolated chamber. Upon ignition of this propellant charge, a disk isolating the propellant charge from the cylinder is ruptured and the propellant gasses flow into the cylinder, mixing with the gasses contained therein. Coinciding with this mixture, gas continues to flow out through the manifold. As the propellant charge burns, pressure within the cylinder will increase sufficiently to break the disk in the manifold's main flow channel. Consequently, the flow rate of the gas into the air bag reaches a maximum level. Although the Bishop patent discloses a variable deployment rate of an air bag, the variable deployment rate is the result of two electrical signals.
U.S. Pat. No. 3,966,228 to Neuman, issued June 29, 1976, discloses an air bag restraint system in which the rate of deployment of the air bag varies over time. In one embodiment of this invention, there is a first cylinder containing a certain volume of gas under pressure. A manifold connects the first cylinder to the air bag, but a disk having charges contained therein prohibits flow of gasses therebetween. At an end opposite of this disk is a second cylinder in communication with the first cylinder by means of an orifice. The second cylinder thus also initially has gas under pressure equal to that within the first cylinder. When sensors detect a collision, an electrical signal is sent to the charges within the disk. The explosion causes the disk to break and gas begins to flow into the air bag, including gas from the second cylinder which flows into the first cylinder, through the orifice, and into the air bag. Since the cross-sectional area of the orifice is smaller than that of the manifold connecting the first cylinder and the air bag, the pressure in the second cylinder will not decrease as rapidly as the pressure in the first cylinder. When a certain pressure differential between the first and second cylinders is achieved, the piece containing the orifice will break. Upon the breaking of this portion, the flow rate of the gas from the second cylinder into the first cylinder, and eventually into the air bag, will be increased to a maximum level. Although the Neuman patent discloses a variable deployment rate from a single electrical signal together with the use of a pressure differential, there is no disclosure or suggestion of using the pressure differential for the ignition of any type of propellant. Therefore, in order to fully inflate the air bag, a larger volume of gas is needed since no heat is being applied to expand the gas and thereby increase the pressure and flow rate. Relatedly, it is likely that larger cylinders would be required to store the gas.
U.S. Pat. No. 3,895,821 to Schotthoefer et al., issued July 22, 1975, discloses an inflation apparatus for an air bag safety device which uses only a single charge initiated by an electrical signal. In this apparatus, there is an outer cylinder containing a volume of gas under pressure. At the end of the cylinder nearest the inflatable apparatus, namely the air bag, there is a second inner cylinder with a propellant charge. There is a disk isolating the propellant in the inner cylinder from the outer cylinder. The disk also covers discharge ports connecting the outer cylinder to the manifold which is connected to the air bag. Upon sensing a collision, the propellant charge is ignited which causes the rupturing of the disk. Thereafter, the propellant gasses mix with the gas in the outer cylinder and gas begins to flow into the air bag through the ports connecting the outer cylinder to the manifold. Although the Schotthoefer et al. patent discloses using a single electrical signal for deploying an air bag with ignition of a propellant to expand the gas, there is no disclosed delay between an initial flow rate into the air bag and a subsequent larger flow rate into the air bag.
U.S. Pat. No. 4,049,935 to Gruber, issued Sept. 20, 1977, discloses a pressure switch which utilizes a diaphragm. This particular apparatus does not directly relate to the ignition of a propellant charge or other equivalent which will result in initiation of flow into an air bag. The apparatus is merely directed towards a pressure sensing device wherein by use of a diaphragm, a means is provided to generate a warning signal that the air bag safety device is inoperable in its present condition. In particular, there is a diaphragm which has a constant pressure on one side thereof produced by a volume of gas contained in a isolated reference chamber. The opposite side of the diaphragm is subjected to the pressure of the gas in the cylinder which ultimately flows into the air bag. When the inflating apparatus is operable, the pressure in the cylinder is greater than the pressure in the reference chamber. In such a case, the diaphragm is deflected in a position wherein the apparatus is electrically connected so that if a collision occurs, the inflator will operate to inflate or deploy the air bag by operation of a non-disclosed inflating means. However, if the pressure in the cylinder is reduced below a certain level, the diaphragm will deflect as a result of the pressure in the reference chamber exceeding the pressure in the cylinder by a certain amount. This will result in a separate electrical connection which will generate a warning indicating that the inflating apparatus is inoperable in its present condition.
Although the above-discussed references have each contributed to the useful deployment of air bags, a number of deficiencies still exist, which, if corrected, would provide an improved air bag inflator. An object of the present invention is therefore to provide a plurality of features which are directed toward overcoming these deficiencies, particularly by providing a single, compact apparatus which utilizes a single electrical signal to initiate deployment of an air bag, while still utilizing a delayed augmentation of the initial flow rate to fully inflate the air bag. A further object of the present invention is to provide a propellant-augmented inflator which is more simple in construction, has fewer or less expensive component parts, and has all active inflator components on one end of the inflator. Another object of the present invention is to provide an inflator which is more adaptable to programming the gas delivery rate to certain desired criteria and which is temperature compensated to minimize variation in the performance of the inflator due to changes in ambient temperature.